A great variety of multiplex equipment has evolved over the years, since the experimental beginning of frequency division multiplex equipment in 1914, in attempts to make full use of the frequency spectrum available. However, in general, these prior art systems have required the use of common equipment such as carrier supplies for signalling, groups, and super groups. None of the prior art equipment has total flexibility in that none of the prior art equipment provides identical modems without common equipment capable of placing a CCITT (International Telegraph and Telephone Consultative Committee) compatible 4kHz sideband directly onto the baseband frequency spectrum.